Re: [Boost-users] [multi_index] using boost::tuple and hash_unique

From: Joaquín Mª López Muñoz (joaquin_at_[hidden])
Date: 2007-04-23 12:27:17

Ovanes Markarian ha escrito:

> Hello,
>
> unfortunately I can't figure out how to specify member access for a hash function to a hash
> indexed mult-index container containing boost::tuple. I would like to hash by the first tuple
> member only. Can someone help?
>
> Here is an example:
>
> typedef boost::tuples::tuple<std::string, int, some_other_type>    my_tuple;
>
> struct hash {};
>
> multi_index_container<
>    my_tuple
>    , indexed_by<
>        hashed_unique<tag<hash>, ????
>        , other_index_type...
>      >
>    >                                      hashed_container;
>
> I would like this tuple to be hashed by the first member. boost::tuple has no access member
> function to the first member. The only way to access it is:
>
> my_tuple t("aaa", 10, xyz);
>
> std::string s(get<0>(t));
>
> but as I can see the doc for multi_index it supports only access through a member function or by
> using the hash function which is applied to the whole object. The second scenario does not suit
> well, since I must pass an object instance to the hasher, where I would like to pass a name only.
> Should I write my own key_extractor class? Any help is appreciated.

Hello Ovanes, the issue of using a boost::tuple member as a key for
a Boost.MultiIndex index has arisen in the past. Please read the
following posts:

  http://lists.boost.org/boost-users/2005/12/16087.php
  http://lists.boost.org/boost-users/2005/12/16088.php

Do they address your problem? Best regards,

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo